Implantable defibrillators detect the onset of abnormal heart rhythms and apply corrective electrical therapy, specifically one or more bursts of electric current to the heart. A defibrillator assembly includes a set of electrical leads, which extend from a pulse generator housing into the heart. Within the pulse generator housing are a battery for supplying power, monitoring circuitry for detecting abnormal heart rhythms, and a capacitor for delivering the bursts of electric current through the leads to the heart. Since the pulse generator portion of the defibrillator assembly is usually implanted in the left region of the chest or in the abdomen, the leads must extend from that area through veins and into the heart.
During normal daily activity of a patient, the leads must flex through a large number of cycles and withstand various other stresses. Numerous cycles of flexing causes fatigue damage and failure in leads, and other stresses such as axial stress can further cause lead damage. Leads are particularly susceptible to fatigue damage or failure at stress concentration points along the lead. Examples of stress concentration points include, but are not limited to where a lead exits a pulse generator, or where a lead is attached to a more rigid structure such as an electrode. Kinking in a flexural direction and crushing in an axial direction may also be problems in stress concentration points.
Leads may need to follow narrow and tortuous paths which may require short electrodes to navigate tight bends, thus creating more stress concentration points. Additionally, the designed size of leads is decreasing with industry pressure to make less invasive products. Smaller leads tend to be more fragile, which further increases the need for more robust lead designs that can withstand numerous flex cycles and axial stresses.
What is needed is a lead that is more robust and resistant to damage or failure from modes such as fatigue failure, axial damage or failure, or other lead stress failure modes. What is also needed is an electrode and lead design that is flexible and adds axial strength while maintaining a small lead diameter.